v3.25.0.1
RETIREMENT BENEFITS - Changes in Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year $ 13,252 $ 12,602  
Service cost 292 275 $ 412
Interest cost 635 626 408
Benefits paid (728) (744)  
Actuarial gain (887) 493  
Balance at end of year 12,564 13,252 12,602
Change in plan assets      
Fair value of plan assets at beginning of year 14,618 14,218  
Actual return on plan assets 604 1,092  
Employer contributions 65 52  
Benefits paid (728) (744)  
Fair value of plan assets at end of year 14,559 14,618 14,218
Accrued asset 1,995 1,366  
Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 1,386 1,441  
Service cost 15 15 23
Interest cost 65 70 42
Benefits paid (105) (107)  
Actuarial gain (2) (33)  
Balance at end of year 1,359 1,386 1,441
Change in plan assets      
Fair value of plan assets at beginning of year 1,095 998  
Actual return on plan assets 96 131  
Employer contributions 55 73  
Benefits paid (105) (107)  
Fair value of plan assets at end of year 1,141 1,095 998
Accrued asset (218) (291)  
Alabama Power | Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year 3,076 2,906  
Service cost 68 64 99
Interest cost 148 145 96
Benefits paid (162) (155)  
Actuarial gain (222) 116  
Balance at end of year 2,908 3,076 2,906
Change in plan assets      
Fair value of plan assets at beginning of year 3,544 3,427  
Actual return on plan assets 148 260  
Employer contributions 9 11  
Benefits paid (162) (154)  
Fair value of plan assets at end of year 3,539 3,544 3,427
Accrued asset 631 468  
Alabama Power | Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 329 344  
Service cost 4 4 6
Interest cost 16 17 10
Benefits paid (25) (24)  
Actuarial gain 2 (12)  
Balance at end of year 326 329 344
Change in plan assets      
Fair value of plan assets at beginning of year 403 372  
Actual return on plan assets 37 52  
Employer contributions 6 3  
Benefits paid (25) (24)  
Fair value of plan assets at end of year 421 403 372
Accrued asset 95 74  
Georgia Power | Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year 4,009 3,851  
Service cost 70 68 103
Interest cost 191 191 123
Benefits paid (239) (224)  
Actuarial gain (298) 123  
Balance at end of year 3,733 4,009 3,851
Change in plan assets      
Fair value of plan assets at beginning of year 4,571 4,456  
Actual return on plan assets 152 331  
Employer contributions 35 9  
Benefits paid (239) (225)  
Fair value of plan assets at end of year 4,519 4,571 4,456
Accrued asset 786 562  
Georgia Power | Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 489 514  
Service cost 4 4 6
Interest cost 23 25 15
Benefits paid (37) (36)  
Actuarial gain 9 (18)  
Balance at end of year 488 489 514
Change in plan assets      
Fair value of plan assets at beginning of year 410 368  
Actual return on plan assets 34 51  
Employer contributions 13 27  
Benefits paid (37) (36)  
Fair value of plan assets at end of year 420 410 368
Accrued asset (68) (79)  
Mississippi Power | Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year 599 569  
Service cost 12 11 17
Interest cost 29 28 18
Benefits paid (33) (32)  
Actuarial gain (40) 23  
Balance at end of year 567 599 569
Change in plan assets      
Fair value of plan assets at beginning of year 669 649  
Actual return on plan assets 23 50  
Employer contributions 5 2  
Benefits paid (33) (32)  
Fair value of plan assets at end of year 664 669 649
Accrued asset 97 70  
Mississippi Power | Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 57 59  
Service cost 1 1 1
Interest cost 3 3 2
Benefits paid (4) (4)  
Actuarial gain (2) (2)  
Balance at end of year 55 57 59
Change in plan assets      
Fair value of plan assets at beginning of year 25 24  
Actual return on plan assets 0 2  
Employer contributions 3 3  
Benefits paid (4) (4)  
Fair value of plan assets at end of year 24 25 24
Accrued asset (31) (32)  
Southern Power | Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year 177 163  
Service cost 7 6 9
Interest cost 9 8 6
Benefits paid (6) (6)  
Actuarial gain (20) 6  
Balance at end of year 167 177 163
Change in plan assets      
Fair value of plan assets at beginning of year 185 178  
Actual return on plan assets 7 12  
Employer contributions 2 2  
Benefits paid (6) (7)  
Fair value of plan assets at end of year 188 185 178
Accrued asset 21 8  
Southern Power | Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 9 9  
Service cost 0 0 0
Interest cost 0 0 0
Benefits paid (1) (1)  
Actuarial gain 1 1  
Balance at end of year 9 9 9
Change in plan assets      
Fair value of plan assets at beginning of year 0 0  
Actual return on plan assets 0 0  
Employer contributions 1 1  
Benefits paid (1) (1)  
Fair value of plan assets at end of year 0 0 0
Accrued asset (9) (9)  
Southern Company Gas | Pension plans      
Change in benefit obligation      
Benefit obligation at beginning of year 882 868  
Service cost 28 24 34
Interest cost 42 42 28
Benefits paid (46) (104)  
Actuarial gain (64) 52  
Balance at end of year 842 882 868
Change in plan assets      
Fair value of plan assets at beginning of year 980 1,002  
Actual return on plan assets 39 79  
Employer contributions 5 3  
Benefits paid (46) (104)  
Fair value of plan assets at end of year 978 980 1,002
Accrued asset 136 98  
Southern Company Gas | Other postretirement benefit plans      
Change in benefit obligation      
Benefit obligation at beginning of year 172 179  
Service cost 1 1 1
Interest cost 8 9 5
Benefits paid (12) (18)  
Actuarial gain (13) 1  
Balance at end of year 156 172 179
Change in plan assets      
Fair value of plan assets at beginning of year 128 113  
Actual return on plan assets 18 19  
Employer contributions 7 14  
Benefits paid (12) (18)  
Fair value of plan assets at end of year 141 128 $ 113
Accrued asset $ (15) $ (44)